In this historical photo from the U.S. space agency, NASA aerospace engineers Pete Zell (left) and Dr. William Clifton Horne (right), project director are shown preparing a laser light sheet for a flow visualization test on June 3, 1993.

The subject of their test is Pratt & Whitney's Advance Ducted Propulsor (ADP) demonstrator engine in the Full-Scale Aerodynamic Complex (NFAC) 40 x 80 foot Wind Tunnel. Shown standing in the nacelle of the ADP is John Girvin, senior test director at NASA Ames Research Center.

Each weekday, SPACE.com looks back at the history of spaceflight through photos (archive).